I recently replaced my rear brakes after a leaking rear hub seal contaminated the brake shoe linings.  I went through a number of online resources including John Twist videos to come up with what I think is the correct spring configuration and thought this photo might be helpful to anyone doing a brake job.  Specifically, I believe the left "tail" of the lower internal spring fits under the rear parking brake as shown in the photo.  Don't assume the last person who worked on your brakes assembled everything correctly.  

My MG is a '63 with the banjo rear axle (1962-1967), but the rear brake setup is the same for all MGB's with the possible exception of the outer lower spring.  Last year it was sold by Moss for only the banjo rear axles, but now I see it's no longer listed so I'm assuming they decided it must not be needed or perhaps they wanted to simplify and offer the same parts configuration for all MGB's.   The part (17H 8737) is however shown in the official MGB parts manual.